There is a continuing need for fire protection materials that permit dissipation of heat and deter the spread of flames, smoke, vapors and/or heat during a fire. Various materials have been used to protect surfaces from excessive heat and flame, including, among others, insulative materials, endothermic materials, intumescent materials, opacifiers, and so-called “superinsulation materials”.
The use of insulative materials such as ceramic or bio-soluble blankets, felt or thick paper-like material, or mineral wool blankets and boards are problematic because the materials are typically very thick and/or heavy. These materials are bulky and difficult to install. In addition, insulative materials can become detached from surfaces when the heat of a fire expands or destroys the means by which the insulative materials are attached.
Endothermic materials absorb heat, typically by releasing water of hydration, by going through a phase change that absorbs heat (i.e. liquid to gas), or by other physical or chemical change where the reaction requires a net absorption of heat to take place. Infrared opacifiers, such as carbon black, titanium dioxide, iron oxide, or zirconium dioxide, as well as mixtures of these, reduce the radiation contribution to thermal conductivity. When activated, endothermic materials and opacifiers restrict heat transfer and, consequently, keep the cold-face temperature lower than it would be absent such materials.
It is known to provide materials designed to retard the spread of fire and heat by an endothermic reaction. A known fire protection material in the form of semi-rigid or rigid boards or molded sections comprises an endothermic-reactive insulating fibrous material comprising (a) an inorganic endothermic filler which undergoes multiple endothermic reactions; (b) inorganic fiber material; and (c) an organic polymer binder. Another known material comprises an endothermic, flexible, fibrous, fire-protective sheet material made of a composition comprising (a) a refractory inorganic fiber; (b) an organic polymer binder, such as an acrylic resin; and (c) an inorganic, endothermic filler, such as alumina trihydrate, which undergoes an endothermic reaction between about 100° C. to 600° C.
Use of endothermic materials somewhat reduces the thickness problem inherent in insulation systems, but endothermics have their own problems. Due to the fact that the material has water molecules trapped in dry form, the system tends to be quite heavy, may be difficult to install and have high associated labor costs. Also, once installed, these systems are extremely difficult to remove and replace in order to perform maintenance work or to update electrical and communication networks hidden within a surface.
Intumescent materials expand to at least about 1.5 times their original volume upon heating to temperatures typically encountered in fire-like conditions, creating an insulation layer that separates the protected item from the fire. One major advantage of intumescent materials is that the unreacted material is thin and lightweight, and easier to install. Intumescent materials generally comprise a mixture of heat resistant inorganic fibers and an intumescent substance. In the event of a fire, the presence of the intumescent substance causes the intumescent material to expand to form an effective seal against the passage of fire and smoke.
The degree to which the intumescent fire protection material expands is important during a fire event, as the intumescent fire protection material must fill the space it is designed to occupy and must do so at a rapid rate. Accordingly, intumescence at the temperatures commonly encountered in a fire event, rapid rate of expansion, and a high degree of expansion are all desirable performance properties of an intumescent fire protection material. A high degree of expansion ensures that the intumescent fire protection material will expand firmly against the periphery of the opening to be sealed, thereby providing an effective seal against the passage of fire and smoke.
It is important in fire protections applications that, once the fire protection material has expanded in response to exposure to elevated temperatures during a fire, that the material cannot shrink if maintained at the increased temperature or exposed to repeated heating and cooling thermal cycling. Because of the low char strengths of sodium silicate-based materials, shrinkage occurs in both situations. Accordingly, intumescent materials that possess a high degree of expansion and char strength for use in passive fire protection applications, and which do not exhibit substantial shrinkage upon prolonged exposure to elevated temperatures or thermal cycling, are desired.